Chapter 14 - Mendel and the Gene Idea

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Multiple Choice
Identify the choice that best completes the statement or answers the question.

Two plants are crossed, resulting in offspring with a 3:1 ratio for a particular trait. This suggests

a.	that the parents were true-breeding for contrasting traits.
b.	incomplete dominance.
c.	that a blending of traits has occurred.
d.	that the parents were both heterozygous.
e.	that each offspring has the same alleles.

Two characters that appear in a 9:3:3:1 ratio in the

generation should have which of the following properties?

a.	Each of the traits is controlled by single genes.
b.	The genes controlling the characters obey the law of independent assortment.
c.	Each of the genes controlling the characters has two alleles.
d.	Four genes are involved.
e.	Sixteen different phenotypes are possible.

A sexually reproducing animal has two unlinked genes, one for head shape (H) and one for tail length (T). Its genotype is HhTt. Which of the following genotypes is possible in a gamete from this organism?

a.	HT
b.	Hh
c.	HhTt
d.	T
e.	tt

It was important that Mendel examined not just the

generation in his breeding experiments, but the

generation as well, because

a.	he obtained very few progeny, making statistical analysis difficult.
b.	parental traits that were not observed in the reappeared in the .
c.	analysis of the progeny would have allowed him to discover the law of segregation, but not the law of independent assortment.
d.	the dominant phenotypes were visible in the generation, but not in the .
e.	many of the progeny died.

When crossing an organism that is homozygous recessive for a single trait with a heterozygote, what is the chance of producing an offspring with the homozygous recessive phenotype?

a.	0%
b.	25%
c.	50%
d.	75%
e.	100%

Use Figure 14.1 and the following description to answer the questions below.

In a particular plant, leaf color is controlled by gene locus D. Plants with at least one allele D have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding dark-leaved plant is crossed with a light-leaved one, and the

offspring is allowed to self-pollinate. The predicted outcome of the

is diagrammed in the Punnett square shown in Figure 14.1, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square.

Figure 14.1

Which of the boxes marked 1-4 correspond to plants with dark leaves?

a.	1 only
b.	1 and 2
c.	2 and 3
d.	4 only
e.	1, 2, and 3

Which of the boxes correspond to plants with a heterozygous genotype?

a.	1
b.	1 and 2
c.	1, 2, and 3
d.	2 and 3
e.	2, 3, and 4

Which of the plants will be true-breeding?

a.	1 and 4
b.	2 and 3
c.	1—4
d.	1 only
e.	None

Mendel accounted for the observation that traits which had disappeared in the

generation reappeared in the

generation by proposing that

a.	new mutations were frequently generated in the progeny, "reinventing" traits that had been lost in the .
b.	the mechanism controlling the appearance of traits was different between the and the plants.
c.	traits can be dominant or recessive, and the recessive traits were obscured by the dominant ones in the .
d.	the traits were lost in the due to blending of the parental traits.
e.	members of the generation had only one allele for each character, but members of the had two alleles for each character.

10.

Which of the following about the law of segregation is false?

a.	It states that each of two alleles for a given trait segregate into different gametes.
b.	It can be explained by the segregation of homologous chromosomes during meiosis.
c.	It can account for the 3:1 ratio seen in the generation of Mendel's crosses.
d.	It can be used to predict the likelihood of transmission of certain genetic diseases within families.
e.	It is a method that can be used to determine the number of chromosomes in a plant.

11.

The fact that all seven of the pea plant traits studied by Mendel obeyed the principle of independent assortment most probably indicates which of the following?

a.	None of the traits obeyed the law of segregation.
b.	The diploid number of chromosomes in the pea plants was 7.
c.	All of the genes controlling the traits were located on the same chromosome.
d.	All of the genes controlling the traits behaved as if they were on different chromosomes.
e.	The formation of gametes in plants occurs by mitosis only.

12.

Mendel was able to draw his ideas of segregation and independent assortment because of the influence of which of the following?

a.	His reading and discussion of Darwin's Origin of Species
b.	The understanding of particulate inheritance he learned from renowned scientists of his time
c.	His discussions of heredity with his colleagues at major universities
d.	His reading of the scientific literature current in the field
e.	His experiments with the breeding of plants such as peas

13.

Mendel's observation of the segregation of alleles in gamete formation has its basis in which of the following phases of cell division?

a.	Prophase I of meiosis
b.	Prophase II of meiosis
c.	Metaphase I of meiosis
d.	Anaphase I of meiosis
e.	Anaphase of mitosis

14.

Mendel's second law of independent assortment has its basis in which of the following events of meiosis I?

a.	Synapsis of homologous chromosomes
b.	Crossing over
c.	Alignment of tetrads at the equator
d.	Separation of homologs at anaphase
e.	Separation of cells at telophase

15.

Black fur in mice (B) is dominant to brown fur (b). Short tails (T) are dominant to long tails (t). What fraction of the progeny of the cross BbTt ´ BBtt will have black fur and long tails?

a.	1/16
b.	3/16
c.	3/8
d.	1/2
e.	9/16

16.

In certain plants, tall is dominant to short. If a heterozygous plant is crossed with a homozygous tall plant, what is the probability that the offspring will be short?

a.	1
b.	1/2
c.	1/4
d.	1/6
e.	0

17.

Two true-breeding stocks of pea plants are crossed. One parent has red, axial flowers and the other has white, terminal flowers; all

individuals have red, axial flowers. The genes for flower color and location assort independently. If 1,000

offspring resulted from the cross, approximately how many of them would you expect to have red, terminal flowers?

a.	65
b.	190
c.	250
d.	565
e.	750

18.

In a cross AaBbCc ´ AaBbCc, what is the probability of producing the genotype AABBCC?

a.	1/4
b.	1/8
c.	1/16
d.	1/32
e.	1/64

19.

Given the parents AABBCc ´ AabbCc, assume simple dominance and independent assortment. What proportion of the progeny will be expected to phenotypically resemble the first parent?

a.	1/4
b.	1/8
c.	3/4
d.	3/8
e.	1

Use the following information to answer the questions below.

Labrador retrievers are black, brown, or yellow. In a cross of a black female with a brown male, results can be either all black puppies, 1/2 black to 1/2 brown puppies, or 3/4 black to 1/4 yellow puppies.

20.

These results indicate which of the following?

a.	Brown is dominant to black.
b.	Black is dominant to brown and to yellow.
c.	Yellow is dominant to black.
d.	There is incomplete dominance.
e.	Epistasis is involved.

21.

How many genes must be responsible for these coat colors in Labrador retrievers?

a.	1
b.	2
c.	3
d.	4

22.

In one type cross of black ´ black, the results were as follows:

9/16 black
4/16 yellow
3/16 brown

The genotype aabb must result in which of the following?

a.	Black
b.	Brown
c.	Yellow
d.	A lethal result

Use the following information to answer the questions below.

Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The part of the radish we eat may be oval or long, with long being the dominant characteristic.

23.

If true-breeding red long radishes are crossed with true breeding white oval radishes, the

will be expected to be which of the following?

a.	Red and long
b.	Red and oval
c.	White and long
d.	Purple and long
e.	Purple and oval

24.

In the

generation of the above cross, which of the following phenotypic ratios would be expected?

a.	9:3:3:1
b.	9:4:3
c.	1:1:1:1
d.	1:1:1:1:1:1
e.	6:3:3:2:1:1

25.

Drosophila (fruit flies) usually have long wings (+) but mutations in two different genes can result in bent wings (bt) or vestigial wings (vg). If a homozygous bent wing fly is mated with a homozygous vestigial wing fly, which of the following offspring would you expect?

a.	All +bt +vg heterozygotes
b.	1/2 bent and 1/2 vestigial flies
c.	All homozygous + flies
d.	3/4 bent to 1/4 vestigial ratio
e.	1/2 bent and vestigial to 1/2 normal

26.

The flower color trait in radishes is an example of which of the following?

a.	A multiple allelic system
b.	Sex linkage
c.	Codominance
d.	Incomplete dominance
e.	Epistasis

27.

A 1:2:1 phenotypic ratio in the

generation of a monohybrid cross is a sign of

a.	complete dominance.
b.	multiple alleles.
c.	incomplete dominance.
d.	polygenic inheritance.
e.	pleiotropy.

28.

In snapdragons, heterozygotes for one of the genes have pink flowers, whereas homozygotes have red or white flowers. When plants with red flowers are crossed with plants with white flowers, what proportion of the offspring will have pink flowers?

a.	0%
b.	25%
c.	50%
d.	75%
e.	100%

29.

Tallness (T) in snapdragons is dominant to dwarfness (t), while red (R) flower color is dominant to white (r). The heterozygous condition results in pink (Rr) flower color. A dwarf, red snapdragon is crossed with a plant homozygous for tallness and white flowers. What are the genotype and phenotype of the

individuals?

a.	ttRr–dwarf and pink
b.	ttrr–dwarf and white
c.	TtRr–tall and red
d.	TtRr–tall and pink
e.	TTRR–tall and red

30.

In cattle, roan coat color (mixed red and white hairs) occurs in the heterozygous (Rr) offspring of red (RR) and white (rr) homozygotes. Which of the following crosses would produce offspring in the ratio of 1 red : 2 roan : 1 white?

a.	red ´ white
b.	roan ´ roan
c.	white ´ roan
d.	red ´ roan
e.	The answer cannot be determined from the information provided.

Refer to the following to answer the questions below.

Gene S controls the sharpness of spines in a type of cactus. Cactuses with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cactuses have dull spines. At the same time, a second gene, N, determines whether cactuses have spines. Homozygous recessive nn cactuses have no spines at all.

31.

The relationship between genes S and N is an example of

a.	incomplete dominance.
b.	epistasis.
c.	complete dominance.
d.	pleiotropy.
e.	codominance.

32.

A cross between a true-breeding sharp-spined cactus and a spineless cactus would produce

a.	all sharp-spined progeny.
b.	50% sharp-spined, 50% dull-spined progeny.
c.	25% sharp-spined, 50% dull-spined, 25% spineless progeny
d.	all spineless progeny.
e.	It is impossible to determine the phenotypes of the progeny.

33.

If doubly heterozygous SsNn cactuses were allowed to self-pollinate, the

would segregate in which of the following ratios?

a.	3 sharp-spined : 1 spineless
b.	1 sharp-spined : 2 dull-spined : 1 spineless
c.	1 sharp spined : 1 dull-spined : 1 spineless
d.	1 sharp-spined : 1 dull-spined
e.	9 sharp-spined : 3 dull-spined : 4 spineless

Use the information given here to answer the following questions.

Feather color in budgies is determined by two different genes Y and B, one for pigment on the outside and one for the inside of the feather. YYBB, YyBB, or YYBb is green; yyBB or yyBb is blue; YYbb or Yybb is yellow; and yybb is white.

34.

A blue budgie is crossed with a white budgie. Which of the following results is not possible?

a.	Green offspring only
b.	Yellow offspring only
c.	Blue offspring only
d.	Green and yellow offspring
e.	a 9:3:3:1 ratio

35.

Which of the following is an example of polygenic inheritance?

a.	Pink flowers in snapdragons
b.	The ABO blood groups in humans
c.	Huntington's disease in humans
d.	White and purple flower color in peas
e.	Skin pigmentation in humans

36.

Huntington's disease is a dominant condition with late age of onset in humans. If one parent has the disease, what is the probability that his or her child will have the disease?

a.	1
b.	3/4
c.	1/2
d.	1/4
e.	0

37.

A woman has six sons. The chance that her next child will be a daughter is

a.	1.
b.	0.
c.	1/2.
d.	1/6.
e.	5/6.

The following questions refer to the pedigree chart in Figure 14.2 for a family, some of whose members exhibit the dominant trait, wooly hair. Affected individuals are indicated by an open square or circle.

Figure 14.2

38.

What is the genotype of individual II-5?

a.	WW
b.	Ww
c.	ww
d.	WW or ww
e.	ww or Ww

39.

What is the likelihood that the progeny of IV-3 and IV-4 will have wooly hair?

a.	0%
b.	25%
c.	50%
d.	75%
e.	100%

40.

What is the probability that individual III-1 is Ww?

a.	3/4
b.	1/4
c.	2/4
d.	2/3
e.	1

41.

People with sickle-cell trait

a.	are heterozygous for the sickle-cell allele.
b.	are usually healthy.
c.	have increased resistance to malaria.
d.	produce normal and abnormal hemoglobin.
e.	All of the above

42.

When a disease is said to have a multifactorial basis, it means that

a.	both genetic and environmental factors contribute to the disease.
b.	it is caused by a gene with a large number of alleles.
c.	it affects a large number of people.
d.	it has many different symptoms.
e.	it tends to skip a generation.

43.

An ideal procedure for fetal testing in humans would have which of the following features?

a.	Lowest risk procedure that would provide the most reliable information
b.	The procedure that can test for the greatest number of traits at once
c.	A procedure that provides a 3D image of the fetus
d.	The procedure that can be performed at the earliest time in the pregnancy
e.	A procedure that could test for the carrier status of the fetus

44.

A scientist discovers a DNA-based test for the allele of a particular gene. This and only this allele, if homozygous, produces an effect that results in death at or about the time of birth. Of the following, which is the best use of this discovery?

a.	To screen all newborns of an at-risk population
b.	To design a test for identifying heterozygous carriers of the allele
c.	To introduce a normal allele into deficient newborns
d.	To follow the segregation of the allele during meiosis
e.	To test school-age children for the disorder

45.

The frequency of heterozygosity for the sickle cell anemia allele is unusually high, presumably because this reduces the frequency of malaria. Such a relationship is related to which of the following?

a.	Mendel's law of independent assortment
b.	Mendel's law of segregation
c.	Darwin's explanation of natural selection
d.	Darwin's observations of competition
e.	The malarial parasite changing the allele

46.

Cystic fibrosis (CF) is a Mendelian disorder in the human population that is inherited as a recessive. Two normal parents have two children with CF. The probability of their next child being normal for this characteristic is which of the following?

a.	0
b.	1/2
c.	1/4
d.	3/4
e.	1/8

47.

Phenylketonuria (PKU) is a recessive human disorder in which an individual cannot appropriately metabolize a particular amino acid. This amino acid is not otherwise produced by humans. Therefore the most efficient and effective treatment is which of the following?

a.	Feed them the substrate that can be metabolized into this amino acid.
b.	Transfuse the patients with blood from unaffected donors.
c.	Regulate the diet of the affected persons to severely limit the uptake of the amino acid.
d.	Feed the patients the missing enzymes in a regular cycle, i.e., twice per week.

48.

Hutchinson-Gilford progeria is an exceedingly rare human genetic disorder in which there is very early senility, and death, usually of coronary artery disease, at an average age of approximately 13. Patients, who look very old even as children, do not live to reproduce. Which of the following represents the most likely assumption?

a.	All cases must occur in relatives; therefore, there must be only one mutant allele.
b.	Successive generations of a family will continue to have more and more cases over time.
c.	The disorder may be due to mutation in a single protein-coding gene.
d.	Each patient will have had at least one affected family member in a previous generation.
e.	The disease is autosomal dominant.

49.

A pedigree analysis for a given disorder's occurrence in a family shows that, although both parents of an affected child are normal, each of the parents has had affected relatives with the same condition. The disorder is then which of the following?

a.	Recessive
b.	Dominant
c.	Incompletely dominant
d.	Maternally inherited
e.	A new mutation

50.

One of two major forms of a human condition called neurofibromatosis (NF 1) is inherited as a dominant, although it may be either mildly to very severely expressed. If a young child is the first in her family to be diagnosed, which of the following is the best explanation?

a.	The mother carries the gene but does not express it at all.
b.	One of the parents has very mild expression of the gene.
c.	The condition skipped a generation in the family.
d.	The child has a different allele of the gene than the parents.